Henderson-Hasselbalch Calculator

The Henderson-Hasselbalch Calculator estimates the pH of a buffer solution using the pKa value and concentrations of acid and conjugate base. This tool helps chemistry students and lab technicians quickly determine buffer stability for precise experiments. Whether you are preparing biological samples, performing titration analysis, or formulating pharmaceuticals, this calculator provides accurate, instant results to streamline your workflow.

Enter the acid dissociation constant (pKa) of the weak acid
Enter the concentration of the conjugate base in molarity (M)
Enter the concentration of the weak acid in molarity (M)
Enter the temperature in Celsius (default is 25°C)

How pH Is Calculated

pH measures how acidic or basic a solution is on a scale from 0 to 14. The calculation relies on the Henderson-Hasselbalch equation, which relates the pH to the acid dissociation constant (pKa) and the ratio of chemical species in the buffer.

pH = pKa + log10([A-]/[HA])

Where:

  • pKa = Acid dissociation constant
  • [A-] = Concentration of conjugate base
  • [HA] = Concentration of weak acid

To find the result, you first calculate the ratio of the base concentration to the acid concentration. Then, you find the base-10 logarithm of that ratio. Finally, you add this logarithm value to the pKa. This method is scientifically accurate for dilute solutions where ideal behavior is expected.

What Your pH Means

The resulting number tells you the acidity or alkalinity of your specific buffer mixture. Understanding this value helps you predict how your solution will react in different chemical environments.

Maximum Buffer Capacity: If your calculated pH is exactly equal to your pKa value, your ratio of base to acid is 1:1. This is the sweet spot where your buffer can resist pH changes the most effectively. For example, a pKa of 4.76 works best at pH 4.76.

Effective Range: A buffer is generally useful within one pH unit of its pKa value. If your pKa is 4.76, your buffer will work well for any target pH between 3.76 and 5.76. Outside this range, the solution loses its ability to neutralize added acids or bases.

Important: Temperature can slightly shift the pKa of weak acids, which affects the final pH. Always check if your experiment requires strict temperature controls.

Disclaimer: This calculator is intended for educational and informational purposes only. Results are theoretical approximations for ideal conditions. For critical laboratory work or pharmaceutical applications, always verify pH using a calibrated meter and consult with a qualified professional.

For the best results, measure your actual pH after mixing to confirm it matches your calculation, and adjust concentrations if necessary.